1. Field of the Invention
The present invention relates to an electro-photographic image forming apparatus and a method of determining a charging voltage. More particularly, the present invention relates to an electro-photographic image forming apparatus for determining a proper charging voltage to correct for deviations in a charged electric potential based on a transfer voltage supplied at a transfer roller, and a method thereof.
2. Description of the Related Art
A conventional image forming apparatus, such as a laser beam printer and LED print head printer (LPH), utilizes electro-photographic technology. Electro-photographic image forming apparatuses perform image forming operations by the processes of charging, scanning, developing, transferring and fixing.
The conventional electro-photographic image forming apparatus includes a photoconductive drum, a charge roller, a laser scanning unit (LSU), a developer roller, a transfer roller and a high voltage power supply (HVPS).
A first step of forming an image using the electro-photographic image forming apparatus is a charging process. In the charging process, a constant charged electric potential must be stably maintained in order to achieve uniformity of the image.
More specifically, if a surface electric potential on a photoconductive drum is unstably maintained while performing a printing operation, images recorded on a recording printing media have an inconstant concentration, thereby resulting in the images having degraded quality. Therefore, it is very important to supply a constant charging voltage to a charge roller in order to uniformly maintain a surface electric potential on a photoconductive drum.
Although a constant charging voltage is supplied to the charge roller, the charged electric potential varies according to the transfer voltage supplied to the transfer roller.
Accordingly, there is a need for an improved method of correcting for the deviation of charged electric potential due to the transfer voltage in the electro-photographic image forming apparatus, and an apparatus employing the method.